1. Field of the Invention
The present invention relates to a hydraulic brake system, in which a pressure in at least one wheel brake cylinder of the hydraulic brake system is adjusted by means of a volume adaptation device and an actuating device. A pressure adjustment may be undertaken individually for each wheel, in particular, and within the framework of an anti-lock brake control, a phase of active pressure buildup and/or a regenerative braking operation.
2. Description of the Related Art
Published European patent application document EP 0292648 A2 discloses a brake system having an anti-lock braking control, which essentially is made up of a hydraulic brake pressure generator actuated by a pedal, a brake-pressure modulator installed in the pressure-means paths between the brake pressure generator and the wheel brakes, with whose aid the brake pressure is variable via a volume change of a chamber containing the hydraulic medium. In such systems the path of the pressure medium from the brake pressure generator to the affected wheel brake is blocked as soon as the rotation behavior of the wheel indicates a locking tendency, and the volume of a chamber which contains an enclosed hydraulic medium and which is connected to the wheel brake is expanded with the aid of a supplementary force. In this described brake system the driver is cut off from the hydraulic braking system in an antilock control. This may cause him to perceive a hard brake pedal, which may be irritating to a driver.
The published German patent application document DE 3317629 A1 relates to a method for controlling a brake system of a vehicle, especially road vehicles, providing brake-slip control, in which the pedal force, together with a supplementary force, is transmitted to a master brake cylinder and from there to the individual wheel brake cylinders via a plurality of pressure means paths which are able to be blocked independently of each other. In addition, the wheel rotation behavior and the vehicle speed or a variable corresponding to the vehicle speed are furthermore measured, the signals are logically linked and processed and then analyzed in order to generate control signals. In the control case, i.e., when a locking tendency arises at a wheel, these control signals are used for lowering the brake pressure at the wheels, for keeping it constant or for increasing it individually or as a group, as a function of the wheel rotation behavior.
Brake systems as described in the mentioned printed publications may produce different pedal feels in the described pressure regulation, which may be perceived as annoying by the driver.